failed to execute this c++ code on android

Question

i am trying to call native opengl methods from java. Everything compiles ok but i still get this horrible error in android log cat

ERROR/AndroidRuntime(536): java.lang.UnsatisfiedLinkError:init
                          at com.deo.Glut.Init(Native Method)

according to oracle

UnsatisfiedLinkError is Thrown if the Java Virtual Machine cannot find an appropriate native-language definition of a method declared native

i can't figure out why the emulator is failing to find my native methods. //the native methods in glut.cpp (jni/glut.cpp)

#include<jni.h>//compiled using cgwin and ndk-build on windows xp
#include<gles/gl.h>
#include<math.h>

static void gluPerspective(GLfloat fovy, GLfloat aspect,
               GLfloat zNear, GLfloat zFar)//android ndk lacks glu tool kit (unbelievable)
{
    #define PI 3.1415926535897932f
    GLfloat xmin, xmax, ymin, ymax;

    ymax = zNear * (GLfloat)tan(fovy * PI / 360);
    ymin = -ymax;
    xmin = ymin * aspect;
    xmax = ymax * aspect;

    glFrustumx((GLfixed)(xmin * 65536), (GLfixed)(xmax * 65536),
               (GLfixed)(ymin * 65536), (GLfixed)(ymax * 65536),
               (GLfixed)(zNear * 65536), (GLfixed)(zFar * 65536));
    #undef PI
}

JNIEXPORT void JNICALL Java_com_deo_Glut_display
  (JNIEnv *, jobject)
{
glClearColor(1,1,0,1);
glClear(GL_COLOR_BUFFER_BIT);
}

JNIEXPORT void JNICALL Java_com_deo_Glut_reshape
  (JNIEnv *, jobject, jint width, jint height)
{
glViewport(0,0,width,height);
if(height==0)height=1;//prevent a divide by zero error in case it ever tries to occur
glMatrixMode(GL_PROJECTION);
gluPerspective(50,width/height,1,1000);
glMatrixMode(GL_MODELVIEW);
}

JNIEXPORT void JNICALL Java_com_deo_Glut_init
  (JNIEnv *, jobject)
{}

I first declared then tried to call the above methods from java which is causing the error.

package com.deo;
public class Glut//java class that declares my native methods(src\com\deo\Glut.java)
{
    static
    {
       System.loadLibrary("glut");
    }
    public native void display();
    public native void reshape(int width, int height);
    public native void init();//this is somehow generating an error :(
}

then tried to call them from my custom renderer

public Glut myglut;
public   void onSurfaceCreated(GL10 gl, EGLConfig config)
{   myglut= new Glut();
    myglut.init();
}

Please help download link to project files

Answer 1

Because your file is a cpp file, you will need extern "C" { } around your exported functions. Otherwise the compiler will mangle the function names and Java won't find the ones it's looking for.